Influence of prey behavior on selective predation by lake trout (Salvelinus namaycush) under laboratory conditions

We explored whether certain behaviors by prey fish species contributed to s elective predation by lake trout (Salvelinus namaycush). Schooling behavior , reactive distance, and predator attack and prey escape swimming speeds we re examined for alewife (Alosa pseudoharengus), bloater (Coregonus hoyi), r ainbow smelt (Osmerus mordax), and yellow perch (Perca flavescens). In addi tion, two- and three-prey species combinations were presented to lake trout to determine if a particular prey species was utilized to a greater extent than others and to observe which specific behaviors or other prey characte ristics could account for their greater utilization. There was little diffe rence in percent capture of various prey species and no significant differe nce (p > 0.05) in escape swimming speeds or attack swimming speeds. However , maximum attack swimming speeds by the lake trout exceeded the maximum esc ape swimming speeds of prey. Average escape swimming speeds ranged from 2.5 to 2.9 m/sec, and average attack swimming speeds ranged from 2.8 to 3.1 m/ sec. Reactive distances were not important since more than 90% of the prey were captured before they had time to react. Prey reactive distances ranged from 0.0 to 1.0 m. Even a small reactive distance and an average escape sw imming speed allowed the prey to get dose to the aquarium wall where lake t rout would not attack. In two-species trials, bloater was preferred over ye llow perch (p < 0.025) in one trial. In three-species trials, lake trout fo raged preferentially (p < 0.05) on alewife when compared to bloater and yel low perch in four of five trials. The bloater appeared as the second most u tilized species although there was no significant difference (p > 0.05) in utilization between bloater and yellow perch. Lake trout were probably reac ting to the continuous movement and tight schooling of alewives in the wate r column.